1. Field of the Invention
This invention relates generally to a binding and gripping unit for the edge of material and more particularly to improved binding unit that provides clamping pressure after a stack of material has been inserted into the binding unit which clamping pressure can be released to allow the removal of the stack of material without damage.
2. Description of the Prior Art
Some prior proposed devices for binding sheet materials have required that each sheet be perforated adjacent to one edge margin. If sheets are to be added, deleted or rearranged, the existing sheets must be removed from the device and then reinserted onto the device. Often the perforations in the sheets become torn with the result that a sheet may fall out of the assembled stack.
Other prior devices for binding sheet materials required that the stack of sheets be forced in between the clamping members to grip the inserted stack of papers and hold the sheets bound at the edge. Often this same resiliency causes the clamping members to damage the sheets as they are forced in between the clamping members. As the resiliency must be weak enough to allow the stack to be inserted, it is often weak enough to allow the stack to become dislodged during normal shuffling of the document.
Certain prior art structures have attempted to alleviate this condition. One such device as shown in U.S. Pat. No. 3,845,521 shows an adjustable binding unit that allows the gripping edges to be adjusted to accomodate a larger stack of materials. But the material must still be wedged between the gripping edges with the same magnitude of force that will hold the material resulting in damage to the material if the force is great or scattering of the material if the force is insufficient to hold the material during normal use.
U.S. Pat. Nos. 586,937, 2,282,565, and 2,869,210 show binding units that open to accept loose-leaf materials without perforations but are designed for heavy duty applications to display materials and none are proven to be completely satisfactory for the binding of small reports.
U.S. Pat. Nos. 3,665,563 and 3,698,043 show other binding units that are light weight and open to accept loose-leaf materials but are designed to be used in a plurality of units to prepare materials for display. Unless the units are tied together they will cause portions of the materials to be folded under with resulting damage to the loose-leaf materials.